Wednesday, 26 June 2013

Release of methane and earthquakes

Sea of Okhotsk


4 June, 2013

On May 29 and June 2, 2013, sudden peak levels of methane in the atmosphere were registered of respectively 2241 and 2238 ppb at an altitude of 33,647.8 ft (10,255.8 mi). Such very high levels are unusual, particularly at such a high altitude. What could have caused this?




Image by Sam Carana, adapted from screenshot from USGS.gov

A magnitude 8.3 earthquake hit the Sea of Okhotsk on May 24, 2013. Depth was over 378.4 mi (608.9 km).

Earthquakes at such a depth can be felt at great distances from the epicenter. Across Siberia, tremors were felt and buildings trembled. In Moscow, some 4500 miles (7242 km) away, local law enforcement officers evacuated 850 people from two apartment buildings after residents said the buildings were shaking, reported the NYTimes.

Screenshot from USGS.gov
This earthquake and the aftershocks (above image) could have caused methane hydrates in the Sea of Okhotsk to become destabilized. Due to the long travel from the bottom of the sea to the sea surface, much of the methane may have been broken down by methane-eating bacteria without entering the atmosphere. Nonetheless, large amounts of methane may reached the atmosphere, causing the above peak readings.

Particularly dangerous is the possibility that such a massive earthquake could trigger earthquakes further north, since a fault line connects the Sea of Okhotsk with the Laptev Sea, while a 5.4 magnitude earthquake (in blue on map above) did hit Siberia on this fault line earlier, i.e. on May 24, 2013.

Without action, levels of methane in the atmosphere can be expected to continue to rise around the world. There are some well-known reasons for this, such as emissions due to wildfires, due to tracking and due to a growing appetite for meat in developing countries. Some less-known reasons include increased methane emissions from:

Melting permafrost - As the permafrost melts, it will be less capable to act as a cap that prevents originating from hydrates to enter the atmosphere, as discussed in more detail  in a recent post.

Aquifers - Water in aquifers can contain high levels of dissolved methane. A hotter planet will see crop yields fall while increasing the need for irrigation, as has been concluded by studies such as this Rice University and the University of California at Davis study. Pumping up more water will come with more methane escaping from aquifers.

Less oxygen in water - As levels of free oxygen in water decrease, there is less opportunity for methane-eating bacteria to break down methane in the water. This is particularly important in case of large abrupt releases of methane from hydrates. A two-part study by Berkeley Lab and Los Alamos National Laboratory shows that, as global temperature increases and oceans warm, methane releases from clathrates would over time cause depletion of oxygen, nutrients, and trace metals needed by methane-eating microbes, resulting in ever more methane escaping into the air without being broken down in the water, as also described in an earlier post.



Accordingly, as above image shows, high levels of methane are projected for the Sea of Okhotsk by this study. 



To get a better idea of the scale of the threat, a study published in 2010 points at pockmarks up to 11 km (6.8 mi) wide off the coast of New Zealand, in an area prone to earthquakes, indicating that large emissions from methane hydrates did occur in the past. The image below is from the April 2013 Press Release 




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